Explosive compositions comprising ammonium nitrate have been widely used throughout the world for many years. As ammonium nitrate is not readily detonatable in and of itself, it is typically mixed with carbonaceous fuels in order to obtain a mixture which is detonatable. Additional compounds such as sensitizers, densifiers, modifiers and surfactants may also be added to an ANFO explosive composition to improve various properties of the explosive composition including the sensitivity to detonation of the explosive, the energy of the explosion and the flowability of the explosive composition.
Typically, explosive compositions containing ammonium nitrate are manufactured at the location where they are to be utilized. For example, an ANFO explosive composition could be prepared at a mine and immediately loaded into a series of boreholes. The ANFO explosive composition would be loaded into the boreholes (typically from about 10 to 15 holes to more than about 100 holes) over a period of days. Typically, an ANFO explosive composition may be kept in a borehole anywhere from one hour up to fourteen days prior to being detonated. If the explosive is a prepackaged explosive composition, then due to shipping and handling time, the explosive composition must be stable for extended periods of time. A prepackaged explosive may also be stored for an extended period of time in a borehole prior to detonation. In some cases, the length of time between mixing the explosive composition and detonation of the explosive composition may be up to ninety days.
After being drilled, a borehole may remain dry for an extended period of time. However, in some cases, water will accumulate in boreholes, such as from the inflow of ground water. ANFO explosive compositions are adversely affected by water penetration and water absorption. Accordingly, if an ANFO explosive composition is loaded into a wet borehole or a borehole into which water subsequently seeps prior to detonation, then the ANFO explosive composition may deflagrate or, in fact, fail to detonate.
One approach which has been utilized to address this problem has been to add guar gum or guar gum and a mixture which includes, for example, sulphur and gilsonite (i.e. ADTEC.TM.) to the ammonium nitrate. One disadvantage of this approach is that excessive amounts of guar gum may be required to obtain a sufficient level of water resistance.